Refining fatty oils



ailing.

Patented Jan. 12 1954 UNITEI') STATE i ATENT OFFICE REFINING FATTY OILS ware No Drawing. Application March 29, 1951, Serial No. 218,275

Claims.

This invention relates to a process for purifying animal, marine, and vegetable oils, including the fats and greases, and commonly classified under the general term of fatty oils, i. e. oils from animal, vegetable and marine sources and consisting chiefly of glycerides and esters of fatty acids. It particularly relates to a process for conditioning fatty oils for refining to remove various impurities and otherwise prepare the oil for various uses. More specifically the invention relates to the refining of oils such as those obtained from cottonseed, sesame, sunflower, corn, soybean, coconut, palm, peanut, lard, whale, various fish, fish livers and tallow.

' Undesirable constituents of crude fatty oils, which constituents are herein termed impurities, and which render the oils inedible or less desirable as a food or other product, include free fatty acids, and coloring matter. The term gums, as used herein, is intended to broadly cover resins, phosphatides, mucines, certain carbohydrates, and the like, which normally occur in crude fatty oils. These gums are either in solution in the oil or are in colloidal suspension, or both.

In common practice, the impurities are removed from the oil by the addition of an alkaline refining reagent such as caustic soda. This alkaline reagent reacts with the free fatty acids, forming soapstocl: which can be separated from the oil, such as by gravity or by centrifugal force. An excess of alkali beyond that required to neutralize the free fatty acids is ordinarily used so as to improve the color, and a portion of this excess normally is absorbed into the gums, agglomerating them so that they can be removed with the soapstock.

The losses that occur during the removal of impurities from fatty oils result from:

(1) Neutral oil absorbed in the precipitated gums.

(2) Neutral oil entrained in the soapstock formed by the neutralization of free fatty acids.

(3) Neutral oil saponified into soapstock because of an excess of refining reagent used. This action is autocatalytic, since any soap produced dissolves oil which can react with the unused saponifying reagent already present in the soap to produce more soap.

(4) Emulsification of oil with the soap phase.

Various methods have been tried in an attempt to reduce these losses of neutral oil. One method is to treat the crude oil with sufficient water to hydrate and precipitate the gums, then to separate the gums from the oil, and subsequently to refine. the degummed oil with a refining reagent. By separately removing the gums, it is possible to refine with a smaller excess of alkali, beyond that required to neutralize the free iatty acids, since none of this alkali will be absorbed into gums, because they are no longer present. The reduction in the alkali excess makes it possible to renne with less saponincation of neutral oil. Also the soapstock formed by an alkali treat of degummed oil is less massive (since gums are i an agglomerating agent) and, therefore, entrains less 011. In many cases the combined losses from the degumming and the refining steps are less than if the oil were refined without oegumming, but in either case the gums themselves absorb from 30 to 40 per cent or their Weight of oil, and this oil is not ordinarily recoverable.

Another method for reducing overall losses, is described in S. Patent 2,254,101. In this process water is added to the crude oil in amount suf ficient to hydrate the gums, but these gums are not removed from the oil before the refining reagent is added. The precipitated gums and soapstock are removed together in a single step. By first hydrating the gums so that they will take up their iull complement of water, it is not necessary in this process to use a great excess of alkali, so that here, again, the loss through saponification of neutral oil is reduced, but there is still a neutral oil loss of 30 to 40 per cent by weight of the gums which represents the amount of oil absorbed in the gums.

Another process for reducing refining losses is as illustrated in U. S. Patent 2,190,593. In this process an aqueous refining reagent is added to the oil in sufficient quantity to neutralize the free fatty acids and to hydrate the gums. The mixture is then heated to a temperature in the neighborhood of 200 F., and is fed into a vacuum chamber where the oil is dehydrated, after which additional refining reagent is added to the oil, and the soapstock and gums are separated from the oil by centrifugal force. In this case the application of heat and the dehydration step change the nature of the gums to reduce the losses from that source.

An object of the present invention is to condition fatty oils for refining by treating the gums contained therein so that they will release their natural complement of absorbed oil without the need for the complicated steps of hydration, dehydration, and/or rehydration, preferably while maintaining the oil at a temperature low enough so that there is no danger or injuring the color. In this process, the step that changes the nature of the gums, so that they will release oil, avoids oil under conditions such that it acts on the gums present in the oil in a manner. so that a large portion of the oil dissolved in the gums is released, and does not, therefore, appear asaa refining loss. solution of the polybasic aliphatic acid, the oil can be refined in any desired manner, with or without using an excess of alkali, andwitha resultant surprisingly high yield. For optimum yield it is important that the amount ofwater present be at least approximately just that which will become chemically boundwith the gums. If. the percentage of: water is materially aboveor below that value,.greater losses: are experienced. By chemically bound water is meant water which is so retained. by the; gums asnot to be readily separable therefrom by distillation, as distinguished from water. of. hydration which is readily separable from the gums by distillation.

To determine the amount of water that becomes chemically bound. with the gums, as distinguished from water which merely hydrates the gums, any suitable procedure may be employed of which the following is illustrative.

To a sample of the crude fatty oil is-added, for example, 1 per cent of an aqueous solution of polybasic aliphatic acid of: any desired concentration, e.- g. per centby weight, thus providing for the presence of water of hydration. The mixture is then agitated and heated to a temperature of say 140 F. After maintaining the agitation for an additional time, for example, two minutes, at this temperature, the mixture is centrifuged and the oil decanted. from the separated gums. The recovered gums are' weighed and then heated slowly,v with constant stirring, to boil off water of hydration, and the heating is. continued at boiling untila sudden rise in temperature occurs. The gumsare then cooled, re-weighed, andthe amount. of water chemically bound with the gums (not evaporated at the boiling temperature) is calculated. The amount of Water chemically bound with'the gums varies from oilto oil, but is ordinarily. inthe range of between .1 per cent and .5 per cent'of the oil from which the gumsare recovered. This represents approximately one-quarter of the amount of water utilized for degumming by hydration.

It has been found thatincrease in theamount of polybasic aliphatic acid used inthis process increases the yield of oil. The determination. of the amount to be used, therefore, isusually governed by the relation between the cost of the acid and the value of theadditional oil recovered. Since both acid and water are added to the oil, the latter in definitely controlled. amount, itis convenient to control the amount of. acid-through its percentage solution in the water. In this-connection aqueous solutions of: acid in concentrations of from 10 per centto 5o per cent byweight are highly useful. The percentage.ofiacicllbased on-crude oil by weight should be-at'least.( ;01%, and usually does not exceed 02%, although larger amounts may beused' if desiredi particularly good operating an e isbetween 0.-075% and 9.125%.

After the addition of the. aqueous Examples of polybasic aliphatic acids are citric, tartaric, maleic, malic, oxalic, itaconic, aconitic, tricarballylic, fumaric, succinic, glutaric and adipic acids.

After the admixture of the acid and the water with the oil, the oil may be refined in any desired way, although it is preferred to use. caustic soda, and particularly causticsoda; or relatively high Be, for example to 40 B-., and to use relatively low excess of caustic soda over that necessary to neutralize the free fatty acid, 6. g. from zero to 011 per cent excess on the dry basis by weight of; oil;

Thesoapstock. may be removed from the refined oil by gravity settling, although it is preferred. to use'a continuous process, with a centrifugal separator to take the soapstock out of the oil, since in this manner better yields are obtainable.

The following examples illustrate the operation of. the process and the results obtained.

EXAMPLE 1 Two samplesof. crude peanut oil. having a free fatty acid. content ofv 1.1-. per cent were refined as follows:

The. first sample was heatedwith agitation to F. whereupon sufficient caustic soda of 30 Ee'pwas added to exactly neutralize (by calculation) the free fatty acids present. This was followed by separation of soapstock by. centrifuging.

To the second sample a-quantity of an aqueous solution of citric acid of 39- percent concentration was added in quantity suificient for the water to become chemically bound with'the gums without excess ordeficiency, this. quantity being arrived at by the procedure described above. This was followed by refining with caustic soda in the same manner as inthe caseof the first sam- In- View of the highly. developed: nature of theart of refining fatty oils, savings of the aboveindicated character are. of outstanding importance, and represent a significant advance in the. art-. Comparable results are obtainedwhen substituting other fatt oils, such as those given 1n the foregoing illustrations, in place of: peanut 011, and/or when substituting other polybasic aliphatic acids, such. asthose givenin the. foregoing illustrations, inplace of the citricraciddn the aqueous solution.

Ithasbeen found that when fatty oils are to be subjected to-asecond-refining step, which is generally known in the. art. as re-refining, substantial savings may. be. made in the practice of this .inventioneven thoughthe-residual free fatty acidpresent in thetreatedoil afterthe first refining step is=substantially higher than normal. In other words, in the practice of this invention, the benefits to be derived.-therefrom carry overinto-the re-refining step',.and. permit, in the first refining. step, if desired; a: less drastic treatment with. alkaline: reagent. than normally. can be tolerated whenthisinvention is not employed;

By way of illustration, when vegetable" oils are to be -used for' the-manufacture of shortening,

it is'desirable that the final hydrogenated oil be practically white, which means that the refined oil must be of a very low color. A desirable way to obtain this low color with a minimum of loss is to follow a refining such as described t have with a re-refining, utilizing a small amount of relatively high B. causticsoda which tends to dissolve out the color bodies. This rerefining also further reduces the free fatty acids. When re-refining is done on oil that has been originally refined after the addition of an aqueous solution of a polybasic aliphatic acid in accordance with this invention, the losses from the re-refining are less than when the re-refining is done on oils that have been merely caustic treated without the practice of this invention, even though there may be more residual free fatty acid to remove. The benefits of this invention carry through beyond the first refining, giving an improved yield for both steps, as shown in the following example.

EXAMPLE 2 A cottonseed oil having a free fatty acid content of 4.2 per cent was divided into two portrons. One part was refined with 30 B. caustic soda of the amount calculated to exactly neutralize the free fatty acids, and the refined oil was then re-refined with 2 per cent of 20 B. caustic soda.

The second part was treated with an aqueous solution of citric acid in accordance with this invention before being refined with exactly the same amount of 30 B. caustic soda as in the first case. This refined oil was then re-refined with 2 per cent of 20 B. caustic soda.

In the refining step, the percentage loss when this invention was employed was 3%; per cent less than the percentage loss when this invention was not employed. In the re-refining step, the percentage loss when this invention was employed was 13 per cent less than the percentage loss when this invention was not employed.

The following example illustrates the importance of selecting an aqueous solution of polybasic aliphatic acid having an amount of water approximately just that which will become chemicall bound with the gums.

EXAMPLE 3 Three samples of hydraulically pressed cottonseed oil having a free fatty acid content of 3.7 per cent were refined as follows:

To sample A a quantity of an aqueous solution of citric acid of 26 per cent concentration was added in quantity suiiicient for the water to become chemically bound with the gums Without excess or deficiency, this quantity being arrived at by the procedure described above. The amount of citric acid in the solution represented 0.1 per cent or the oil by weight. This was followed by heating with agitation to 140 F. whereupon sunicient caustic soda of 30 B. was added to exactly neutralize (by calculation) the free fatty acids present. Soapstocx was then separated by centrifuging.

To Sample B a quantity of an aqueous solution of citric acid of 18.6 per cent concentration was added, in quantity to represent 1.216 times the amount of water added to Sample A. The amount of citric acid again represented 0.1 per cent of the oil by weight. This was followed by refining with caustic soda in the same manner as in the case of Sample A.

To Sample a quantity of an aqueous solution of citric acid of 9.8 per cent concentration was added in quantity to represent 3.2 times the amount of water added to Sample A. The amount of citric acid again represented 0.1% of the oil by weight. This was followed by refining with caustic soda in the same manner as in the case of Sample A. The results are shown in. the follow- As pointed out above, differences in refining loss of the nature illustrated are of particular significance, in view of the highly developed nature of the art.

EXAMPLE 4;

Peanut oil containing 1.4 per cent free fatty acid was refined in a continuous process as follows: Crude oil was pumped at a rate of 5,500 pounds per hour through the system. To this oil, which was at a temperature of F., was continuously added per cent of a 20 per cent citric acid solution. The mixture of citric acid solution and crude oil was then continuously heated to 158 F., and 30 B. caustic soda was continuously added to the flowing stream in an amount calculated to neutralize exactly the free fatty acids. The mixture was then promptly fed into a centrifuge having a rotor of 13 diameter (inside), rotating at 6000 R. P. M., and refined oil and separated soapstock were continuously discharged. The refined oil was continuously delivered from the centrifuge to a second centrifuge, and in the flowing stream to the second centrifuge was added 2 per cent of 20 B. lye to act as a re-refining agent to reduce the color and the free fatty acids. The oil discharging from the first refining centrifuge contained 0.15 per cent free fatty acid, and the oil from the rerefining centrifuge contained 0.03 per cent free fatty acid. The overall loss of the whole process, including the both refining steps, was 3.2 per cent.

There is a laboratory test known as the Wesson loss analysis which is used to determine the amount of neutral oil that exists in a sample of crude oil, differentiating between the oil content and other components, such as free fatty acids, gums, etc. The Wesson loss analysis of this sample of oil showed a maximum available oil content of 97.05 per cent. The loss of 3.2 per cent, noted above, represents an oil recovery of 96.8 per cent based on original crude oil.

The above examples show remarkably improved yields both from refining and from re-refining when utilizing the invention.

With proper agitation the aqueous acids can be dispersed into the crude oil in 30 seconds or less, and a longer agitation time is not disadvantageous. Their benefit is also independent of the temperature of the oil when the acids are introduced, or subsequent temperatures used before or after the addition of the refining reagent.

After the polybasic aliphatic acid is added to the crude oil, the oil may be refined by the batch kettle process, or by a continuous centrifugal process or otherwise. Caustic soda or other refining reagent may be used; the oil may be agitated and conditioned after the lye addition; or may be promptly centrifuged without delay; the reagent "treat may be-.mere1y theaamountzcaiculated as necessary to z-neutralizetherfreeefattygacidsioiiless on" more ;1 the oil may. be .heated: beforeor: after theaadditionof the'lrefining reagent; unrefined without: the addition ofa heat; color: may! beare- .moved by. a..single=.refining'-rwith anaexcessxof refining: reagent, or byx a: reerefining: steps TIinese tration; and not of,1imitation.. Accordinelyiit; is

intended that the patent shall covenby suitable expression in the claims; thesvarious features of patentable novelty that resides in the invention.

LcIaim:

1. ,A .process: for treating a gum-containing fatty oil which comprises admixing witlisaid? oil an aqueous solution: of apolybasic :aliphativacid selected from: theigroup; consisting. of: citric; tartaric,1nia1eic., malimoxalic; itaconio; aconitiEgt'r-icarb allylic; fumaric; succinic; glutaric: and adipic acids,. the.v amount; of said aqueous solution thusadmixed v with; said; oiLbeing; such: that. the 2 water thus added; to; said, oil. is" between; approximately 0.1v and 0.5 by, weight ofisaidwiland issapproximately just sufiicient: to.chemicailsncombinawith the gums containedin saidhoilasaidiaqueouszsolution: losingv of a concentration: in; polybasic: ali- 'phatie: acid such that the amount: of; acid on: a

dry: basis: thus; admixedv withithe oil, is-- at; least 0;;0L%: by weightiot saidmil, .andzthereafter refiningzsaidioil';withianaaikaiine refining: agent.

.72; The:processz;ofi claim; L whereinxthe-amoun oitazci'dz-admixedwith thenil;issbetween 0.075 per centzand10125per centby weight: ofsaid oil;

"3:. The process 10f. claim 25 whereinsthe-s-oil; is; a

t vegetable .oil.

43 The process of: claim"; 3; wherein 1 the acid; is citric acid;.

5;. The: process: ofi claim 3; whereintthe; acid: is

.aconiticzacid;

6; A'ISh'erprQcesszof: claim: 3 whereimthe; acid: is tartaric acid.

7;. The process; of claim: &-wherein;. the;=acid:;is itanonimacid.

8;, The: process: of; claim 1' whereinthemefining steps isvconnected. WithTCaUSt'i CiSOdQAOf atfleast220 B. concentration.

9. The process of claimi8 'whereintheamount of caustic soda employed; is" approximately just sufficient to neutralize the free fatty acid content of the oil. 7

10. The process of claim" 9 whereinthe steps asdefined are followed-by an additional-- refining treatment" with caustic-sodaofat least- 20Be'. concentration.

' FRED SNSADLERL,

References Cited in the file of this patent UNITED STATES PATENTS.

Number" Name Date Z-;4-IO',9-26 Bush etal; Nov. 12, 1946 2,551,496 Lange' May. 1, 1951 

1. A PROCESS FOR TREATING A GUM-CONTAINING FATTY OIL WHICH COMPRISES ADMIXING WITH SAID OIL AN AQUEOUS SOLUTION OF A POLYBASIC ALIPHATIC ACID SELECTED FROM THE GROUP CONSISTING OF CITRIC, TARTARIC, MALEIC, MALIC, OXALIC, ITACONIC, ACONITIC, TRICARBALLYLIC, FUMARIC, SUCCINIC, GLUTARIC AND ADIPIC ACIDS, THE AMOUNT OF SAID AQUEOUS SOLUTION THUS ADMIXED WITH SAID OIL BEING SUCH THAT THE WATER THUS ADDED TO SAID OIL IS BETWEEN APPROXIMATELY 0.1 AND 0.5% BY WEIGHT OF SAID OIL AND IS APPROXIMATELY JUST SUFFICIENT TO CHEMICALLY COMBINE WITH THE GUMS CONTAINED IN SAID OIL, SAID AQUEOUS SOLUTION BEING OF A CONCENTRATION IN POLYBASIC ALLPHATIC ACID SUCH THAT THE AMOUNT OF ACID ON A DRY BASIS THUS ADMIXED WITH THE OIL IS AT LEAST 0.01% BY WEIGHT OF SAID OIL, AND THEREAFTER REFINING SAID OIL WITH AN ALKALINE REFINING AGENT. 